Edge.qxd Some ecological factors influencing the breeding success of the Brenton Blue butterfly, Orachrysops niobe (Trimen) (Lepidoptera: Lycaenidae) D.A. EDGE Edge, D.A. 2002. Some ecological factors influencing the breeding success of the Bren- ton Blue butterfly, Orachrysops niobe (Trimen) (Lepidoptera: Lycaenidae). Koedoe 45(2): 19–34. Pretoria. ISSN 0075-6458. The Brenton Blue butterfly, Orachrysops niobe (Trimen, 1862) (Lepidoptera: Lycaenidae), is endemic to the southern Cape and is currently listed as Endangered. This study looks at some of the key ecological factors influencing the breeding success of the species—host plant abundance and condition, nectar sources, climate/ microclimate, and vegetation management techniques. The adult butterfly population was monitored over an entire breeding season; host plants were identified and individually monitored; and egg counts were done. This enabled the effects of a number of different manage- ment techniques to be evaluated (burning, cutting, physical removal of invasive ele- ments, and combinations thereof). A fivefold increase in the population of O. niobe was observed over the breeding season. This increase was positively correlated to a similar increase in host plant abundance in the areas where cutting and physical removal of invasive elements was practiced. Burning, by contrast, appeared to have a negative impact on host plant and butterfly abundance over the same period. Impacts of other fac- tors such as climate, nectar sources and the natural strength of the second brood are dis- cussed. A hypothesis, of megaherbivore activity as the principal historical disturbance mechanism promoting locally favourable conditions for O. niobe to establish and main- tain colonies, is proposed. Recommendations for reserve management and future research are made. Key words: butterfly ecology, endangered species, nectar, population dynamics, popu- lation counts, reserve management. D.A. Edge, School of Environmental Sciences and Development, Potchefstroom Uni- versity, P O Box 2586, Knysna, 6570, Western Cape Province, South Africa. ISSN 0075-6458 19 Koedoe 45/2 (2002) Introduction The Brenton Blue butterfly Orachrysops niobe (Trimen, 1862) (Lepidoptera: Lycaen- idae) is one of South Africa’s most threat- ened butterfly species, being endemic to the southern Cape and currently red-listed as Endangered (Henning & Henning 1995). It is now only known to occur at one locality —at Brenton-on-Sea near Knysna. It previously occurred in Nature’s Valley 50 km to the east but has become extinct there as a result of anthropogenic activities (property develop- ment, habitat fragmentation, prevention of fires, and exclusion of larger herbivores). The colony at Brenton-on-Sea has been sub- ject to similar pressures but has been given a reprieve from a similar fate following a pro- tracted and highly publicised campaign to save the species (Steenkamp & Stein 1999). This has resulted in the procurement of the land on which the colony occurs by central government and the impending proclamation of a reserve which covers 1.47 ha. Research has been conducted on the life his- tory (Edge & Pringle 1996; Williams 1996); butterfly population size and distribution (Britton & Silberbauer 1997); the ant popula- tions found at the site (Robertson 1997, 1998, 2000); and on the floristics and plant communities (Lubke et al. 1996). Case histories from other endangered butter- fly species (mostly from the northern hemi- Edge.qxd 2005/12/09 10:02 Page 19 sphere) have shown that it is essential to understand the ecology of each endangered butterfly species in detail if conservation efforts are to succeed (New 1997). The aim of the current research is to deter- mine some of the critical ecological factors influencing the breeding success of O. niobe. Since Edge & Pringle (1996) demonstrated by rearing adult O. niobe from ova that the larvae are essentially phytophagous the abundance and condition of the sole larval host plant Indigofera erecta Thunberg is one of the factors examined in detail. Several vegetation management techniques to pro- mote proliferation of the host plant have been proposed by other workers (Lubke et al. 1996; Schutte-Vlok 2001), and their effi- cacy needs to be tested. Other factors dealt with in the present study are nectar sources and preferences; the influence of climate; and the population dynamics of O. niobe. Study site The study site is the Brenton Blue butterfly reserve, situated in Brenton-on-Sea near Knysna (34º04'20''S; 23º02'00''E) in the Western Cape Province of South Africa (Fig. 1). This figure is to scale and depicts areas that were treated as well as the network of paths that were cut. The reserve has a total area of 14 673 m². Koedoe 45/2 (2002) 20 ISSN 0075-6458 Fig. 1. Brenton Blue Butterfly Reserve, near Knysna. Edge.qxd 2005/12/09 10:02 Page 20 The reserve is bounded to the north by a tarred road, W.K. Grobler Drive. To the north of this road is a public open space, Uitzicht 216 Portion 81, which is owned by the Dis- trict Municipality. To the south, the reserve boundary is Fynbosoord, a tarred access road to the residential properties which lie south of Fynbosoord and at the south-eastern cor- ner of the reserve. The reserve is bounded on the west by residential properties and stands, and Mountain Rose Drive. The eastern boundary abuts partly on residential proper- ty and partly onto public open space that does not presently form part of the reserve. The study site is on a well-drained south (seaward) facing slope of average inclination of 1 in 4. It is at an altitude of 95 m to 120 m and is 450 m from the sea. The geology, cli- mate and floristics of the site were described by Lubke et al. (1996). The vegetation can be characterised as asteraceous coastal fyn- bos with patches of candlewood-dominated thickets [Pterocelastrus tricuspidatus (Lam- ont) Sonder]. Materials and methods Habitat modification Habitat modifications (treatments) were carried out in the areas indicated on the site plan (Fig. 1) and summarised in Table 1. The procedure for the burn on 20 September 2000 was described by Hiseman (2000). The “skoffeling” treatment applied to Area B involved cutting down of the bracken fern (Pteridi- um aquilinium (Linnaeus) Kuhn), and turning over the surface layer down to a depth of 0.2 m so that the roots of the bracken were pulled out. The intention was to simulate the activities of bush pigs, which it had been hypothesised by Schutte-Vlok (2001) played an important role in the past in controlling the bracken fern. The network of access paths (Area D) were cut during the period from 4–25 July 2001, using shears at a level of approximately 10 cm above the ground, to a width of 1–1.5 m. The paths wind to avoid larger bushes and trees and any patches of the host plant I. erecta, and have been subsequently kept open by pulling out any new bracken fern plants. The blocks contained within the paths (Area E) have not been disturbed, but difficulty of access has preclud- ed any systematic host plant observations in this study. Area F consists of a steep embankment approximately 1.5 m high running east to west which resulted from excavations for a sewerage line in the early 1990s. Indigofera erecta monitoring Immediately after the fire careful watch was kept for any I. erecta seedlings. As soon as they appeared they were marked and identified with 1-m sticks and numbered tags. Thereafter, during host plant sur- veys, any new plant which had sprouted was similar- ly identified. These plants were given a letter fol- lowing the number to show that they were not amongst the original cohort. When the paths were cut all existing I. erecta plants exposed were also marked, as were the new ones that germinated and/or sprouted later on. No distinction was made as to whether the new plant had originat- ed from seed or had resprouted from an old root stock. ISSN 0075-6458 21 Koedoe 45/2 (2002) Table 1 Summary of treatment areas Treatment Area (m²) Description of treatment A 1400 Burnt on 20 September 2000. Natural succession thereafter. B 1000 Burnt on 20 September 2000. “Skoffeled” prior to fire, natural succession thereafter. C 300 Burnt on 20 September 2000. Bracken fern controlled by manually pulling new plants out for 6 months thereafter. D 1500 Network of access paths cut through the unburnt portion of the reserve, and kept open thereafter. E 10450 Undisturbed, unburnt blocks inside paths F 120 Steep 1.5 m high embankment created by excavation for sewerage line in early 1990s Edge.qxd 2005/12/09 10:02 Page 21 Surveys of all the identified I. erecta plants were conducted at regular intervals (19 March, 9 May, 18 July, 25 July, 10 October, 10–25 November 2001 and 28 January–1 March 2002). During the March and May surveys the health of each plant was recorded. This was a subjective measure made by eye on a scale from 1 to 10, and took into account the overall size of the plant and its stolons, withering of leaves and stems, and whether the plant appeared to be spreading or shrinking. From July the size of each plant was recorded by counting the number of stolons and the number of inflorescences. A stolon, for the purpose of this study, is defined as an aerial shoot of the plant (horizontal or vertical) which orig- inates near the root stock. Stolons vary in length from 150 mm to 500 mm. The inflorescences of I. erecta are vertical racemes that carry the flowers on sturdy peduncles. Figure 2 is a diagrammatic sketch of a typical plant (the detailed morphology of the root system is not yet known). Adult butterfly population counts In 2000 and 2001 experiments by the author with mark, release, recapture (MRR) techniques had shown that the trauma to the butterflies caused by this method posed an unacceptable risk to the small and fragile population. Consequently a transect method was devised, using the network of paths, to yield a comparative count of butterflies which could be used to assess population trends. This method required similar weather conditions (sunny, warm, little wind) and was carried out at the same time each day (11:30–12:30). The route through the network was the same for each count, at a fairly constant pace of 20 m/min., and took about one hour, allowing some time for stops to record significant observa- tions such as nectar plant visitation, oviposition or mating. During the population counts all adults seen were recorded with the place, gender and activity. Multi- ple sightings of a particular insect inevitably took place but each sighting was recorded. The observa- tions for each day were recorded on a data sheet that has a schematic layout of the paths in the reserve incorporated and shows the traverse route (Fig. 3). A second counting method was used which is referred to as the “fixed point” method. The observ- er was positioned at point A2 (which is on the nor- mal male patrolling route) and recorded all O. niobe that came within 10 metres of this point during a 30 minute period (at the same time each day). The fixed point method was “calibrated” on several separate occasions by capturing all the butterflies present and retaining them in a gauze netting cage. This enabled a relationship to be derived between the “fixed point” count and the total population of but- terflies patrolling (referred to as the repetition factor for this method). Repetition factor = Total count made / actual butter- flies present Koedoe 45/2 (2002) 22 ISSN 0075-6458 Fig. 2. Typical growth form of Indigofera erecta (diagrammatic). Edge.qxd 2005/12/09 10:02 Page 22 The repetition factor for the transect method could only be estimated (as between 1.25 and 2.0). The butterflies on the paths were much less mobile than the patrolling males mostly seen from the fixed point and the observer moved quickly along each path, reducing the chance of repeat observations of the same insect. Observations made during the transects that fell within the “fixed point” area (defined as the three paths observable from the fixed point A2) were treated as if they were made during a fixed point count for the purpose of applying a repetition factor and calculating the actual butterflies present. Adult butterfly behaviour During the adult butterfly counts and the plant sur- veys, all noteworthy adult butterfly behaviour was recorded. Categories were defined as fluttering (typ- ical slow female flight within 15 cm of the ground or vegetation); patrolling (more vigorous male flight up to a metre from the ground or over vegetation); mate search and acquisition (males only); nectar plant vis- itation (plant species and butterfly gender recorded); host plant search; oviposition (plant number record- ed); copulation (time and location recorded); bask- ing, and resting. ISSN 0075-6458 23 Koedoe 45/2 (2002) Early stages (eggs, larvae) All the identified host plants were searched thor- oughly during the period from 10–25 November 2001 and again from 28 January–1 March 2002 for eggs and larvae. The search method involved exam- ining both sides of each stolon. In order to standard- ise the search about one minute was taken to search each stolon. When eggs or larvae were found the host plant number was recorded with the count and any unusual features (e.g., eggs were usually laid on the lower surface of a leaf—so if they were in anoth- er position this was recorded). Eggs were recorded as unhatched (pale blue, entire) or hatched (white ring of eggshell remnant). Climate and microclimate Rainfall records from the previous ten years were obtained from a weather station located at 140 Wat- sonia Road, Brenton-on-Sea. This station is situated at 90 m altitude, 400 m from the sea, and 500 m away from point A1 in a westerly direction and is also sited on a south-facing slope. An additional weather station was established at the site (position near A1 as shown on Fig. 1) and daily recordings commenced in June 2001. Data recorded was mm rainfall using a conical rain gauge and the maximum and minimum temperatures using a ther- mometer. The only microclimate factor recorded during the present study was a subjective estimate by eye of the Fig. 3. Data sheet incorporates a schematic layout of the paths in the reserve and shows the traverse route. Edge.qxd 2005/12/09 10:02 Page 23 Koedoe 45/2 (2002) 24 ISSN 0075-6458 Table 2 Plants and stolons of Indigofera erecta counted in each area between March 2001 and February 2002 Treatment area Original a Plants per 100 m² Stolons per 100 m² Plants/ Oct Nov Feb Oct Nov Feb 100 m² 2001 2001 2002 2001 2001 2002 Fire/ bracken control (C) 16.3 16.7 19.0 14.0 32 82 54 Fire/ no control (A) 1.7 1.9 2.0 1.9 10 26 13 Embankment (F) 10.0 13.3 15.0 14.2 62 128 92 Paths in unburnt area (D) 7.0 8.5 12.7 14.3 24 109 133 TOTALS 5.7 6.6 8.9 9.0 20 72 73 a Start date for areas (C), (A) and (F) was 19 March 2001, and for area (D) was 25 July 2001. Table 3 Shade factors, population and growth records of I. erecta in each treatment area Treatment area Shade Original New Deaths Percentage increase in % plants plants stolons counted a Fire/ bracken control (C) 22.4 49 17 24 68 Fire/ no bracken control (A) 47.6 24 5 3 24 Embankment (F) 81.2 12 9 4 49 Paths in unburnt area (D) 38.3 105 121 12 463 Totals/Averages 38.6 190 152 43 265 a Defined as: (Final stolon count - initial stolon count) / (Initial stolon count) x 100 Table 4 Orachrysops niobe total adult population counts between October 2001 and March 2002, using two methods and standardised as counts per hour First brood Second brood Date Total count /h Date Total count/h Transects Fixed point Transects Fixed point 29.10.01 3.81 12.0 14.01.02 1.60 08.11.01 4.86 13.3 28.01.02 19.09 42.9 09.11.01 4.55 30.01.02 15.86 63.2 10.11.01 4.07 12.0 04.02.02 18.21 35.0 11.11.01 5.41 17.1 08.02.02 11.79 54.0 12.11.01 4.20 27.0 13.02.02 19.29 87.0 13.11.01 3.85 10.5 17.02.02 13.58 39.0 16.11.01 4.76 11.4 26.02.02 4.14 18.0 18.11.01 3.53 6.0 08.03.02 2.67 Averages 4.34 13.7 Averages 11.8 42.9 Edge.qxd 2005/12/09 10:02 Page 24 maximum and minimum temperatures using a ther- mometer. The only microclimate factor recorded during the present study was a subjective estimate by eye of the extent of shade at each host plant site, ranging from 0 % (no shade for whole day) to 100 % (full shade for whole day). Results Indigofera erecta monitoring The number of living I. erecta plants located and the number of stolons counted in each treatment area at different dates is given in Table 2, and a summary of the I. erecta microclimate and population dynamics data gathered appears in Table 3. Adult butterfly population counts A summary of the data obtained using the two comparative methods (transect and fixed point) is presented in Table 4. Each day’s count using the two methods has been stan- dardised to a count per hour so that the fig- ures for each day are directly comparable. No butterflies were observed between 21 November 2001 and 10 January 2002. Table 5 presents the total counts from the two methods taken over six days, during the peak emergence of each brood with favourable weather conditions. These results are another assessment of the relative strength of the two broods. Table 6 presents the results of calculations made from the observations to determine the sex ratio of the adults (assuming a repetition ISSN 0075-6458 25 Koedoe 45/2 (2002) Table 5 Orachrysops niobe adult population counts for six days at the peak of the November 2001 and February 2002 broods using two counting methods Period of Surveys Entire Reserve Transects Fixed Point A2 (11:30-12:30) (20 minutes per day) Males Females Totals Males Females Totals November 2001 (1st brood) 12 17 29 25 2 27 Jan/Feb 2002 (2nd brood) 39 54 93 99 14 113 Ratios (2nd:1st brood) 3.25 3.18 3.21 3.96 7.0 4.19 Table 6 Calculation of O. niobe sex ratios during the November 2001 and February 2002 broods (male and female) November 2001 brood February 2002 brood Method/area Transect Fixed Total Transect Fixed Total Time (mins) 740 276 1016 450 195 645 Male count 20.5 44.5 65 22.8 135.2 158 Female count 25.6 7.4 33 63.3 16.7 80 Repetition/ hr 1.25 6.56 1.25 6.56 Actual male/h 1.330 1.475 2.805 2.432 6.341 8.773 Actual female/h 1.661 0.245 1.906 6.752 0.783 7.535 Male:Female ratio 0.80 6.02 1.47 0.36 8.10 1.16 Edge.qxd 2005/12/09 10:02 Page 25 Koedoe 45/2 (2002) 26 ISSN 0075-6458 Fig. 4. O. niobe comparative population counts using the fixed point method. Fig. 5. O. niobe comparative population counts using the transect method. Table 7 Orachrysops niobe egg counts in each treatment area during November 2001 and January/February 2002 (H = hatched eggs and U = unhatched eggs) Treatment areas Period of surveys Increase 10 Nov. 2001 - 25 Nov. 2001 28 Jan. 2002 - 27 Feb. 2002 factor 1st–2nd H U Totals H U Totals brood Fire/ bracken control (C) 2 0 2 15 1 16 8.00 Fire/ no bracken control (A) 2 7 9 10 11 21 2.33 Embankment (F) 3 1 4 11 2 13 3.25 Paths in unburnt area (D) 106 109 215 440 606 1046 4.87 Totals 113 117 230 476 620 1096 4.76 factor of 1.25 for the transect method). The repetition factor for the fixed point method was determined to be 6.6. The overall male to female ratio in the colony falls within the range from 1.2 to 1.5. If a repetition factor for the transect method of 2.0 is used the male to female ratio falls within the range 1.6 to 1.8. Figures 4 and 5 present graphically the pop- ulation fluctuations over a 21 weeks period from 17 October 2001 to 12 March 2002, using the two methods. Oviposition The I. erecta plants preferred for oviposition were mostly healthy and vigorous, on well drained sloping ground and in semi shade with bare ground in the immediate vicinity of the plant. The eggs were usually laid on the underside of leaves on a horizontal stolon close to the ground. The eggs were therefore well con- cealed and in a cool, damp microclimate. Only occasionally (3.2 % of observations) were eggs laid on the upper surface of the leaves, on stems (as opposed to leaves) or on vertical stolons (as opposed to horizontal stolons). The egg counts (H = hatched and U = unhatched) for each brood are presented in Table 7. The data from Tables 7 & 2 can be used to calculate egg densities (per plant and per stolon) for each treatment area as shown in Table 8. Edge.qxd 2005/12/09 10:02 Page 26 ISSN 0075-6458 27 Koedoe 45/2 (2002) Table 8 Orachrysops niobe average egg densities per plant and per stolon in each treatment area during November 2001 and January/ February 2002 Areas Period of surveys 10 Nov. 2001–25 Nov. 2001 28 Jan. 2002 –27 Feb. 2002 Per 100 plants Per 100 stolons Per 100 plants Per 100 stolons Fire/ bracken control (C) 0.035 0.008 0.38 0.10 Fire/ no bracken control (A) 0.32 0.02 0.81 0.12 Embankment (F) 0.22 0.026 0.77 0.12 Paths (D) 1.13 0.13 4.89 0.53 TOTALS 0.78 0.096 3.65 0.45 Table 9 Nectar sources and visitations by O niobe adults Plant species Family Number of Months Areas Flower Symmetry b visitations a colour Commelina africana L. COMMELINACEAE 2F February D2 Yellow Z Hypoxis villosa L. HYPOXIDACEAE 1F November C1 Yellow A Felicia echinata (Thunb.) ASTERACEAE 1M February C1 Lilac & A yellow Lobelia tomentosa L. f. CAMPANULACEAE 1M;3F January A1;C2 February D1 Blue Z Erica speciosa Andrews ERICACEAE 2F January D2 Red A Indigofera erecta Thunb. FABACEAE 1F November D1 Pink Z Indigofera verrucosa FABACEAE 2M;3F January Eckl.& Zeyh. February C5 Pink Z Rhynchosia caribea (Jacq.) FABACEAE 1M February C1 Yellow Z Rhynchosia chrysoscias FABACEAE 6M;6F November - C8 Benth. ex Harv. February D4 Yellow Z Geranium incanum Burm. GERANIACEAE 3M;2F November C4 A1 Lilac A Sebaea aurea (L.f.) Roem. & Schult. GENTIANACEAE 1M November A1 Yellow A Polygala fruticosa P.J.Bergius POLYGALACEAE 1F February D1 Purple Z Selago glomerata Thunb. SELAGINACEAE 8M;12F January C15 A February 3 D2 Pale blue A Totals 10 Families 23M A6 C37 33F D13 a M = male and F = female b A = actinomorphic and Z = zygomorphic Nectar plant visitation A summary of the observations made of O. niobe adults visiting nectar plants appears in Table 9. Thirteen angiosperm species were recorded from 10 different families, with Selago glomerata Thunberg being the most frequently selected nectar source (35.7 % of observations). Actinomorphic (radially sym- metrical) flowers were narrowly preferred over zygomorphic (bilaterally symmetrical) flowers (53.6 %) and lilac or pale blue flow- Edge.qxd 2005/12/09 10:02 Page 27 ers were chosen over other colours (57.1 %). The majority of the nectar plant visitation observations were made in the burnt areas (76.8 %), where the preferred nectar plants (which were mostly forbs) were more abun- dant. Climate The weather data in Table 10 was obtained from the 140 Watsonia Road weather station (rainfall); the weather station at the reserve (rainfall and temperatures); and the Knysna records of S.A. Weather Services (SAWS). The Watsonia Road and reserve stations agreed for rainfall records over fourteen months to within 1.5 %. There is also good agreement between the Watsonia Road sta- tion and SAWS over the longer term. Overall comparison of the burnt areas ver- sus the paths Drawing the data together from the various sources in this study the summary compiled in Table 11 was produced. Discussion Reproduction and growth of Indigofera erecta The genus Indigofera is large, with 78 species occurring in the Cape Floristic Region (CFR) and 720–730 worldwide (Goldblatt & Manning 2000). The taxonomy is still being actively researched and Goldblatt & Man- ning identify 19 undescribed species in the CFR (24 % of the total). A variety of repro- ductive strategies are evident in the genus, Koedoe 45/2 (2002) 28 ISSN 0075-6458 Table 10 Weather records for the Knysna area Month 140 Watsonia Road Brenton Blue Knysna - S.A. rainfall (mm) a butterfly reserve b Weather Service c Max. Min. Mean Rainfall Average Average Rainfall Average Average mean max. min mean max. min mm °C ° C mm °C ° C January 82 21 52.4 53 28.6 14.5 56.8 26.2 17.1 February 85 12 47.3 16 28.4 14.9 47.9 27.2 16.7 March 107 6 57.0 14 26.8 15.5 59.7 27.1 17.0 April 122 0 60.8 37 24.8 13.2 65.7 20.1 10.1 May 128 6 51.3 62 20.4 10.7 64.7 21.4 11.4 June 74 8 34.3 44 17.4 8.4 64.0 19.5 8.3 July 117 18 61.0 62 17.5 9.0 60.9 19.0 8.7 August 200 0 85.2 103 20.5 9.9 84.6 20.1 10.0 September 216 35 61.7 54 19.9 10.9 64.7 20.9 11.9 October 192 25 87.4 42 22.8 13.5 74.2 22.9 14.7 November 122 0 87.3 85 24.9 13.8 59.0 23.3 15.9 December 144 12 62.5 53 27.8 15.1 50.8 24.9 17.1 Annual 1078 564 756.3 625 753.1 a from January 1992 to August 2002 b from July 2001 to August 2002 c from January 1951 to August 2002 Edge.qxd 2005/12/09 10:02 Page 28 ISSN 0075-6458 29 Koedoe 45/2 (2002) Table 11 Summary of data comparing the burnt areas with the paths Description of data Burnt areas Paths A, B &C (Area D) Total area (m²) 2700 1500 Final I. erecta stolons count 341 1988 Final I. erecta stolons per 100 m² 13 130 I. erecta stolon increase (%) 41.5 463 O. niobe eggs laid per 100 m² (November) 0.4 14.3 O. niobe eggs laid per 100 m² (February) 1.3 70 O. niobe eggs laid per plant (November) 0.129 1.13 O. niobe eggs laid per plant (February) 0.544 4.89 % of total O. niobe eggs laid (November) 6.5 93.5 % of total O. niobe eggs laid (February) 4.6 95.4 % of male O. niobe sightings (November) 69.0 31.0 % of female O. niobe sightings (November) 22.2 77.8 % of male O. niobe sightings (February) 31.1 68.9 % of female O. niobe sightings (February) 10.6 89.4 Adult O. niobe nectar visitations 43 13 Average shading factor (%) 43 38 with six species being described as resprout- ing and six as reseeding shrubs or shrublets. The biology and phenology of I. erecta have not yet been studied as far as can be ascer- tained. Two other Indigofera species have been identified at the site (I. verrucosa and I. glaucescens Ecklon & Zeyher). Schutte-Vlok (2001) hypothesised that the germination of I. erecta was principally fire induced, and used this as one of the main arguments for management of the reserve by regular controlled burns. Jeffrey et al. (1997) found that not all legume species tested ger- minated in response to dry heat treatment and hypothesised that species found in dune or forest communities, which were less fire prone, required other stimuli to break seed dormancy. Cocks & Stock (1997), in a study of germination stimulation of 16 Fabaceae species, found that response to fire varied and seemed to be correlated with certain seed characteristics. Observations and experimentation on the host plant of Orachrysops ariadne (Butler, 1898) - which is Indigofera woodii H.Bolus var. laxa — indicated that whilst fire and heat seemed to play a role in seed germination, seedlings emerged in unburned areas as well as burnt areas. (Lu & Samways 2002b). The evidence accumulated in the present study indicates that the germination of I. erecta is stimulated not only by fire as expected (Table 3—areas A and C—“new plant” column) but also by surface distur- bance and by removal of competing plants to admit more light (access paths—area D). Effects similar to this could have been caused naturally in the past by megaherbi- vores creating paths for access and passage, and by their browsing and grazing on the plants along the paths. Elephants may have occasionally visited the area in the past and their partiality to many typical fynbos plants as well as P. tricuspidatus, and the rhizomes of P. aquilinium has been recorded recently in fynbos areas adjacent to the Knysna forest (Milewski 2002). It is interesting that these two species have a tendency to proliferate at the study site in the absence of any control agent(s). At the study site the predominant growth form of I. erecta is depicted diagrammatical- ly in Fig. 2. Most of the vegetative mass is contained in the horizontal stolons, which are Edge.qxd 2005/12/09 10:02 Page 29 Koedoe 45/2 (2002) 30 ISSN 0075-6458 up to 500mm long and spread along the ground in a horizontal or downward direc- tion, depending on the slope of the ground. Vertical stolons are much less frequent and appear to be a response to there being greater ground cover by competing plants in the vicinity. Since the stems of I. erecta are herbaceous the height of the vertical stolons is limited to 100mm by their mechanical strength unless support is gained from neigh- bouring plants, in which case a height of a metre or more can be attained. Leaves are sparser on these vertical stolons compared to the horizontal stolons, which are supported by the ground and therefore able to bear many more leaves. The growth form described above is marked- ly different from the host plant of O. ariadne which is an upright plant growing to over a metre and which has woody stems (Lu & Samways 2001). This type of growth form can compete successfully with taller plants and does not require bare ground to grow vig- orously which appears to be the case with I. erecta. The influence of growth form can be seen by comparing the response of I. erecta to fire as opposed to cutting and clearing around the plant. The I. erecta plants that sprouted after the fire did well at first, while the ground was bare and there was not much shade. Howev- er they were out-competed later as the ground became covered with grass and sedge species and the taller more vigorous species (P. aquilinium, Helichrysum spp, Rhyncosia spp, etc) shaded out the smaller I. erecta plants. Consequently growth of both horizon- tal and vertical stolons was inhibited and not only did a high proportion of I. erecta plants die during the observation period (refer to Table 3), but also the overall increase in the number of stolons was low. By contrast the I. erecta plants which were present on the paths, together with those that sprouted subsequently, had a much lower mortality and a far greater rate of increase in the number of stolons (refer to Tables 2 & 3). This shows clearly that growth of I. erecta was encouraged to a far greater extent by the activity (disturbance) of cutting the access paths rather than by the fire. It is noteworthy that parts of the reserve area were regularly disturbed in the 1980s and early 1990s by the property owner - who used to cut down the taller plants every few years to gain access for surveying. Escom also used to keep the strip of ground along their power servitude just below the present W. K. Grob- ler Drive open for maintenance access. These sort of activities may have been critical sus- taining factors for the butterfly at the site over the last two decades. Orachrysops niobe adult population fluctu- ations The author has been keeping records of adult population counts dating back to 1993. In that year, using a method similar to but not as rigorous as in the present study, a maximum count of 10/h was obtained for the November brood using a fixed point observation method. In November 2000 the maximum count was 16/h also using a fixed point method, and in November 2001 the maxi- mum count was 15/h. It can therefore be stat- ed with reasonable confidence that the November population of adult O. niobe has not shown any significant decline over the eight year period, and if anything seems to have increased. However, in previous years, whilst the author has sparse records for December, January and February, a major second brood such as emerged in February 2002 has never been detected, with at most a hand full of individ- uals being seen. The three to four fold increase in the adult numbers between November 2001and February 2002 (Figs. 4 & 5), and the nearly five fold increase in the egg counts between the two broods, show that O. niobe is strongly bivoltine if favourable conditions exist, with early and late summer emergences. This contrasts greatly with O. ariadne which is univoltine and only emerges in autumn (April/May). (Lu & Samways 2001) Edge.qxd 2005/12/09 10:02 Page 30 There are undoubtedly many other factors which control the population of O. niobe, such as predation and parasitism in the larval stage; the influence of the larval-ant relation- ship and the availability of sufficient ant colonies in proximity to the host plant con- centrations. These factors are beyond the scope of the present study but will be the focus of future investigations. Oviposition preferences of O. niobe All members of the genus Orachrysops so far studied in any detail appear to specialise on a single larval host plant in the genus Indigofera (refer to Table 12). In the case of the four colonies of O. ariadne studied by Lu & Samways (2001, 2002a) they found that an abundance of the host plant was an essential pre-condition for a colony to become established and to be maintained. The abundance of I. erecta at the Brenton Blue butterfly reserve is greater than at any other place on the Brenton peninsular, and indeed greater than all other sites investigat- ed for the presence of O. niobe over a num- ber of years. (Ball 1997) An earlier study of oviposition sites found that the host plant and egg densities varied across the reserve (Britton & Silberbauer 1997), but were generally positively corre- lated. A similarly patchy distribution of host plant has been found in the present study, with the females concentrating their oviposi- tion activities in areas containing the most host plant. In the present study, both in the November and February broods the majority of the eggs were laid on the host plants growing on the paths, and the density of eggs per plant and per stolon were also much higher on these host plants. The preference of the females of O. niobe for oviposition on host plants on or near the paths as opposed to plants in the burnt areas could have the following possible causes: - The very high density of host plant in some areas of the paths attracted the females by sight and smell. - Predominance on the paths of horizontal stolons close to the ground which are preferred by the females. - Accessibility of the host plants on the paths - no need to flutter between other plants. - Health and vigour of the host plants on the paths (see Table 3). - More favourable microclimate for larval survival may exist along the paths (shel- tered, cool and humid). - Presence of an (as yet unknown) host ant in these areas. It was concluded from a study of the habitat of the endangered Lycaenid Aloeides den- tatis dentatis (Swierstra, 1909) that this but- terfly had a preference for a disturbed com- munity in an early stage of succession, which seemed to encourage colonisation by the host ant. (Deutschländer & Bredenkamp 1999). Several observations were made during the present study of oviposition by another poly- ISSN 0075-6458 31 Koedoe 45/2 (2002) Table 12 Larval host plants of Orachrysops species Species Host plant Reference O. lacrimosa (Bethune-Baker, 1923) Indigofera species unknown Clark & Dickson 1971 O. mijburghi Henning & Henning, 1994 Indigofera species unknown Williams 1996 O. niobe (Trimen) I. erecta Thunberg Edge & Pringle 1996 O. brinkmani Heath, 1997 I. declinata E.Meyer Heath 1997 O. ariadne (Butler) I. woodii var. laxa H. Bolus Lu & Samways 2001 O. subravus Henning & Henning, 1994 I. woodii var. woodii H. Bolus Lu & Samways 2001 Edge.qxd 2005/12/09 10:02 Page 31 ommatine Lycaenid Lampides boeticus (Lin- naeus, 1767) on the reserve and in all cases this was on the host plant Rhynchosia chrysoscias Bentham ex Harvey, particularly in the burnt area where this climbing shrublet thrives. The niche differentiation between these two closely related butterfly species is clear and reduces potentially harmful larval competition. Nectar sources Nectar sources were hypothesised to be a limiting factor for maintaining colonies of O. ariadne in Natal where only eight nectar plants were identified, with an overwhelm- ing preference for two of them. (Lu & Samways 2001). The wider variety of flow- ers used by O. niobe (13 species) and their relative abundance at the study site leads one to surmise that this is not currently a limiting factor for the population. Furthermore the wide choice of flowers of different symme- try, morphology, size and colour indicates that O. niobe is a generalist which does not fulfil any pollination function and is thus a nectar thief. The dominance of forbs and thus nectar plant visitations in the burnt area is probably because the woodier shrubs had not yet gained ascendancy in the succession process. Influence of climate and microclimate From Table 10 it can be seen that rainfall was well below the average for previous years during the period from October 2001 to March 2002, which is the emergence time for adult O. niobe. The increase in butterfly population that has been recorded in this study took place despite the adverse dry and hot conditions. It should be noted that mois- ture appears to be a critical factor in all Orachrysops species studied so far (Pringle 1997; Lu & Samways 2001) From a microclimate point of view, the shade factor and the angle of slope are two of the most important factors. It can be seen from Table 3 that the butterfly larval host plant does better in intermediate shade (approx. 40 %) situations. Generally the area where the paths were cut had a steeper slope than the burnt area and this made for a cool- er microclimate as well as good drainage. Overall comparison of burning versus cut- ting The summary in Table 11 clearly demon- strates that the cut access paths created a superior habitat for both I. erecta to grow and for O. niobe to breed. The burnt area did however provide more male O. niobe activ- ity, principally because it included the cur- rent patrolling path of the males. Another important attraction and contribution of the burnt area was as a nectar source because of the prevalence of nectar rich forbs in the early successional stages after a fire. This may have some significance in the overall ecology of the butterfly and needs to be taken into account. Conclusions The germination of the host plant Indigofera erecta is not just fire induced. There was a doubling of the number of host plants on the access paths (area D), where no fire had taken place, during the observation period. Indigofera erecta plants in the burnt areas A and C, and on the embankment (area F) had a higher mortality rate than those on the paths. The growth rate of the plants on the paths - measured by increase in the number of stolons - was an order of magnitude high- er than in the burnt area. Orachrysops niobe females had an over- whelming preference to lay eggs on the I erecta plants on or near the access paths and almost completely avoided the plants on the burnt area. There was a significant increase in the population of the butterfly between the first brood and the second brood—three to four times as many adults, and nearly five times as many eggs laid. Orachrysops niobe uses a wide range of nec- tar sources, most of which are abundant at the reserve and not likely to be a limiting Koedoe 45/2 (2002) 32 ISSN 0075-6458 Edge.qxd 2005/12/09 10:02 Page 32 factor in controlling the population, although the higher abundance of nectar sources in the burnt area may have some significance. The rainfall during this season has been sig- nificantly below the historical average so this factor could not have caused the popula- tion increase. The evidence suggests rather that both the proliferation of the host plant on the access paths and the increase in the butterfly population came about as a result of the access path cutting and maintenance activities. The areas that were burnt have produced relatively small numbers of I erec- ta plants on which hardly any eggs were laid. Under natural conditions the type of distur- bance caused by the cutting of paths is simi- lar to that created by large and small herbi- vores grazing. Burning is likely to cause a short-term negative impact on butterfly pop- ulations since it not only does not create con- ditions suitable for breeding, but the danger exists of larvae perishing in any fire occur- ring during the months from October to April. Recommendations Burning should only be carried out at the reserve in areas where the host plant is absent. The network of paths should be maintained and kept open through the next breeding sea- son in order to continue monitoring of the host plant and to re-assess the butterfly pop- ulation in November 2002. The morphology, reproductive biology (specifically the germination stimuli) and phenology of Indigofera erecta should be studied in detail. The existence of a larval-ant association needs to be confirmed and investigated to find out if this could be a regulating factor on the populations of the butterfly. Acknowledgements My thanks are due to Cape Nature Conservation for permission to work within the Brenton Blue butter- fly reserve, and to Rhett Hiseman in particular for loan of a GPS instrument belonging to Cape Nature Conservation. Professor Brian Allanson is also thanked for his advice on methods to be used and for the use of laboratory equipment belonging to the Knysna Basin project. I am also grateful to Renier Terblanche, Dr Hamish Robertson and Ernest Pringle for their guidance on methods, data analysis, review of drafts and general discussion and encour- agement. Wiehan Properties’ role in making avail- able their records from a weather station at Brenton- on-Sea and Brian Young’s assistance in gathering and compiling of data from the weather station at the Brenton Blue butterfly reserve are also gratefully acknowledged. References BALL, J.B. 1997. Some notes on the Brenton Blue butterfly, Orachrysops niobe (Trimen) (Lepi- doptera, Lycaenidae). Unpubl. research report for the Endangered Wildlife Trust of Southern Africa, Johannesburg - Attachment 1: 22–27. COCKS, M.P. & W.D STOCK. 1997. Heat stimulated germination in relation to seed characteristics in fynbos legumes of the Western Cape Province, South Africa. South African Journal of Botany 63(3): 129–132. BRITTON, D.R. & L.X. SILBERBAUER. 1997. The life- history, ecology and conservation of the Brenton Blue Butterfly, Orachrysops niobe (Trimen) (Lycaenidae) at Brenton-on-Sea. Unpubl. research report for the Endangered Wildlife Trust of Southern Africa, Johannesburg. CLARK, G.C. & C.G.C. DICKSON. 1971. Life histories of the South African Lycaenid butterflies. Cape Town: Purnell. DEUTSCHLÄNDER, M.S. & G.J. BREDENKAMP. 1999. Importance of vegetation analysis in the conser- vation management of the endangered butterfly Aloeides dentatis dentatis (Swierstra) (Lepi- doptera, Lycaenidae). Koedoe 42(2): 1–12. EDGE, D.A. & E.L. PRINGLE. 1996. Notes on the nat- ural history of the Brenton Blue Orachrysops niobe (Trimen) (Lepidoptera: Lycaenidae). Metamorphosis 7(3): 109–20. GOLDBLATT, P. & J. MANNING. 2000. Cape Plants: A conspectus of the Cape flora of South Africa. Pp. 486–492. In: Strelitzia 9. Cape Town: National Botanical Institute of S A & Missouri Botanical Garden. HEATH, A. 1997. Description of a new species of Orachrysops Vári from the Western Cape Province of South Africa (Lepidoptera: Lycaenidae). Metamorphosis 8(1): 26–32. ISSN 0075-6458 33 Koedoe 45/2 (2002) Edge.qxd 2005/12/09 10:02 Page 33 HENNING, G.A. & S.F. HENNING. 1995. Updating the status of South African red data butterfly species. Metamorphosis 6(2): 96– 98. HISEMAN, R.E. 2000. Brenton Blue Butterfly Reserve management report. Internal report for Cape Nature Conservation (unpublished, dated 30 November 2000). JEFFREY, D.J., P.M. HOLMES & A.G. REBELO. 1988. Effects of dry heat on seed germination in select- ed indigenous and alien legume species in South Africa. South African Journal of Botany 54(1): 28–34. LU, S-S. & M.J. SAMWAYS. 2001. Life history of the threatened Karkloof blue butterfly, Orachrysops ariadne (Lepidoptera: Lycaenidae). African Entomology 9(2): 137–151. LU, S-S. & M.J. SAMWAYS. 2002a. Behavioural ecol- ogy of the Karkloof blue butterfly, Orachrysops ariadne (Lepidoptera: Lycaenidae) relevant to its conservation. African Entomology 10(1): 137–147. LU, S-S. & M.J. SAMWAYS. 2002b. Conservation management recommendations for the Karkloof blue butterfly, Orachrysops ariadne (Lepi- doptera: Lycaenidae). African Entomology 10(1): 149–159. LUBKE, R.A., D.B. HOARE & J.E. VICTOR. 1996. The vegetation and floristics of the habitat of the Brenton Blue butterfly. Unpubl. research report for the Endangered Wildlife Trust of Southern Africa, Johannesburg. MILEWSKI, A.V. 2002. Elephants and fynbos. Veld & Flora March 2002: 28. NEW, T.R. 1997. Butterfly Conservation. Melbourne: Oxford University Press. PRINGLE, E.L. 1997. Butterfly breeding areas—a microclimate perspective. Metamophosis 8(2): 82–84. ROBERTSON, H.G. 1997. Report on the ants at Bren- ton-on-Sea and their possible interactions with the Brenton Blue Butterfly, Orachrysops niobe. Unpubl. research report for the Endangered Wildlife Trust of Southern Africa, Johannesburg. ROBERTSON, H.G. 1998. Report on field trip to Bren- ton-on-Sea from 15–26 November 1998. Inter- nal report for Life Sciences Division, South African Museum, Cape Town (unpublished). ROBERTSON, H.G. 2000. Report on field trip to Bren- ton-on-Sea from 6-10 November 2000. Internal report for Life Sciences Division, South African Museum, Cape Town. SCHUTTE-VLOK, A.L. 2001. Environmental manage- ment plan for the Brenton Blue Butterfly Reserve. Internal report for Cape Nature Con- servation (unpublished). STEENKAMP, C. & R. STEIN. 1999. The Brenton Blue saga—a case study of South African biodiversity conservation. Johannesburg: Endangered Wild- life Trust/Nedbank/Danish co-operation for Environment and Development. TRIMEN, R. 1862–1864. On some new species of South African butterflies. Transactions of the Entomological Society, London, 3rd Series Vol I: 279–291. WILLIAMS, M.C. 1996. Report on research findings concerning the Life History and Ecology of the Brenton Blue (Orachrysops niobe). Metamor- phosis 7(1): 3–7. 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